Discrete component voltage doubler and voltage inverter circuits are well known in the art. Such circuits are used in many electronic systems which require a multiplicity of DC voltages for operation. Hand held portable communication devices are one such example. These devices typically utilize several DC voltages for operation and are developing to utilize lower battery voltages in order to reduce the size and weight of the device. For example, the use of a lithium ion battery is expected to reduce the overall size of these portable devices and produce a battery voltage of approximately 3.5 Volts. In addition, the digital circuitry running from lower operating voltages results in a reduction in power dissipation. Voltage multiplying and inverting charge pumps circuit have been developed for increasing the lower battery supply voltages in order to maintain both efficiency and output power in the power amplifiers utilized in these devices.
An example of known inverting charge pump is shown in FIG. 1. This design is known in the art as a H-bridge circuit. This circuit utilizes four switches 4,6,8,10, a pump capacitor 12, and a hold capacitor 14 to generate an output voltage, -V, from an input voltage, +V. The switches are controlled by non-overlapping differential square wave signals, Q and Q'. When the signal Q is high Q' is low, the upper two switches 4,6 are closed and the lower two switches 8,10 are open. This defines a charge cycle. During the charge cycle the pump capacitor 12 is charged to the power supply voltage, +V. When the differential control signals switch Q goes low and Q' goes high, the upper two switches 4,6 open and the lower two switches 8,10 close, resulting in a charge transfer cycle. During the charge transfer cycle the pump capacitor 12 is charged to the power supply voltage +V. A portion of the charge on the pump capacitor 12 is transferred to the hold capacitor 14 and a small negative voltage develops across the hold capacitor. The amount of charge transferred in each charge transfer cycle is governed by the R.sub.on C.sub.p time constant where R.sub.on is the on resistance of the switches and C.sub.p is the capacitance of the pump capacitor 12. As the process continues through several charge and charge transfer cycles, more charge is transferred from the pump capacitor 12 to the hold capacitor 14 until the voltage across the hold capacitor 14 reaches a steady state voltage of negative V. While this circuit provides an inverted output, it does not provide a voltage which is greater in magnitude that the input voltage.
An example of a voltage multiplying and inverting charge pump is shown in U.S. Pat. No. 4,807,104 by Floyd et al. That patent teaches a charge pump circuit for outputting either a positive or a negative output voltage having a predetermined magnitude which is an integral multiple of the magnitude of power supply voltage. The first capacitor is charged to the power supply voltage. The first capacitor is coupled to the power supply voltage to develop a double voltage transfer supply with the supply voltage. Second and third capacitors are charged by the double voltage transfer supply. The second capacitor is used to store the charge from the first capacitor for a continuous output voltage having a magnitude which is twice the magnitude of the power supply. The third capacitor may be reconfigured to generate a negative transfer voltage.
The negative transfer voltage is used to charge a fourth capacitor which provides a negative output voltage with twice the magnitude of the power supply voltage.
For applications requiring only an inverted output voltage which is twice the magnitude of the power supply voltage, a problem exists in that the circuit of figure one does not give a multiple of the input voltage and excess power is dissipated through components placed in the Floyd et al. circuit to achieve various outputs (ie. .sup.+ ZV). Also each additional component requires additional space on the device. It is therefore desirable to reduce the number of components necessary for implementing such a circuit.